The present invention relates to a process for the preparation of aromatic (di)chlorosulphonic acids and (di)bromosulphonic acids. Such aromatic sulphonic acids which are monohalogenated or dihalogenated are intermediates which can be used for a large number of purposes, for example for the preparation of colorants or plant protection agents.
According to previous processes, aromatic sulphonic acids can be chlorinated for example in such a way that the sulphonic acid is brought into contact with chlorine either in a polar solvent such as water or sulphuric acid or in an inert solvent, with the simultaneous presence of a catalyst. The sulphonation of the basic aromatic compound and the chlorination are frequently carried out one after the other in the same reaction batch. Examples of the first-mentioned embodiment are given in EP 57,889 or DE-OS (German Published Specification) 2,501,899. An example which may be mentioned of the second embodiment mentioned is U.S. Pat. No. 4,131,619. Both embodiments mentioned correspond to the ionic mechanism of this chlorination. Both variants have the disadvantage that large amounts of contaminated solvents are obtained which must either be eliminated or worked up for recycling; if a catalyst is simultaneously used, the latter is also to be treated.
There was therefore a demand to have available a process which permits chlorination or bromination of aromatic sulphonic acids without the use of a solvent and a catalyst.